Treated cellulosic material and electrical apparatus embodying the same



A. J.,IPA|.uMBo "E TAL TREATED CELLULOSIC' MATERIAL AND ELECTRICH Fig.l.

Filed 10m. '28; 1965 Fig.2.

Fig.3.

WITNESSES:

United States Patent 3,324,222 TREATED CELLULOSIC MATERIAL ANDELECTRICAL APPARATUS EMBODYING THE SAME Anthony J. Palumbo, Sharon, andJames G. Ford, Sharpsviiie, Pa., assignors to Westinghouse ElectricCorporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Oct.28, 1963, Ser. No. 319,174 4 Claims. (Cl. 17417) paratus. Suchmaterial-s represent a desirable source of electrical insulation fromthe standpoint of their economic advantages over other available typesof insulation. Moreover, cellulosic insulation possesses good physicalproperties, generally speaking and satisfactory initial dielectricstrength.

However, cellulosic materials deteriorate rapidly at temperaturesappreciably above 100 C. when in contact with air or when in contactwith liquid dielectrics such as are used in electrical transformers, forexample oil, where oxidation products include acids which attackcellulosic materials. Both the physical and electrical properties areaifected by this deterioration with the result that the insulationgradually loses its electrical insulating strength and its mechanicalstrength is rapidly dissipated.

The electrical and physical properties of cellulosic material such aspaper, cotton cloth, cotton tape, pressboard and wood deteriorate at anincreasing rate when the temperature is increased above 100 C. whetherexposed to air or in contact with fluid dielectric compositions. Thus,for example, after being immersed for only a few weeks in refinedpetroleum transformer oil at 120 to 150 C. paper will retain practicallynone of its original tensile strength. Generally a length of freshelectrical grade kraft paper may be bent or flexed several hundred timesbefore it will break. However, after only a weeks immersion intransformer oil at 120 C. to 150 C. it will break upon being doublefolded one time.

- This deterioration in physical properties is accompanied by acorresponding decrease in electrical insulat- I ing properties. Forthese reasons it has been specified in the industry that, in electricalapparatus employing cellulosic insulation, for continuous operation thetemperatures not exceed about 105 C.

"ice

Other objects of the invention will be obvious and will appearhereinafter.

For a better understanding of the nature and objects of the inventionreference should be made to the following detailed description whichwill be given with particular reference to the accompanying drawings, inwhich:

FIG. 1 is a View in perspective, partly in cross section, of atransformer core insulated with the novel cellulosic insulation of theinvention; 7

FIG. 2 is a view in elevation partly in cross section, of a transformer;and

FIG. 3 is a view in elevation, partly in cross section, illustrating aninsulated cable.

In accordance with the present invention it is now possible to greatlyincrease the retention of both dielectric strength and mechanicalstrength of cellulosic insulation at elevated temperatures bysubstantially uniformly distributing throughout the insulation effectiveamounts of certain chemical stabilizing compounds. The amounts of thecompounds to be employed may be small, but these small proportionsthereof impart a highly beneficial stabilizing effect to the electricalinsulation. The chemical compounds which have been found to impart theseimprovements are l,5-dihydroxyanthraquinone, and the nitrogen bearingcompounds p-phenylazoaniline, ammelide, 1,3-dimorpholino-Z-propanol,triallylcyanurate, Z-aminothiazole, and polyvinylpyrrolidone. Two ormore of these compounds may be employed simultaneously in stabilizingcellulose.

It is to be noted that, generally speaking, these compounds exhibitsubstantial solubility in water or water and alcohol solutions whichconsiderably enhances their incorporation into cellulosic insulationespecially from an economic standpoint. An exception applies-in the caseof ammelide whose solubility is somewhat less than that of the otherstabilizing compounds of the invention. It is to be also noted thatthese compounds exhibit substantial insolubility in oil whichfacilitates their use in an electrical apparatus employing an oil typeliquid dielectric. Obviously if the compounds were soluble in suchdielectrics they would tend to be depleted from the insulation bydissolution into the dielectric.

Several factors are involved in obtaining the benefits of the invention.First, the chemical stabilization compounds must be present in thecellulosic insulation in amounts within the range of about 0.02% toabout 10% by weight based on the weight of the cellulosic material.

It has now been discovered that there are certain com- -i properties arenot only apparent in the presence of liquid dielectrics but are obtainedas well when the insulation is employed in an atmosphere of air or othergas.

. Accordingly, a primary object of the invention is to provide astabilized cellulosic electrical insulation characterized by bothimproved thermal stability and im-.

proved dielectric integrity.

-A further object of the invention is the provision of improvedcellulosic electrical insulation containing effect ve amounts of certainchemical stabilizing compounds.

Less than .02% stabilization compounds do not impart to the insulationany appreciable improvement in either electrical insulation ormechanical strength at elevated temperatures. The presence of more thanabout 10% of r the compounds is uneconomical and does not appreciablyincrease the degree of improvement beyond that obtained with 10%. Withinthis broader critical range it is preferred to employ about .5 to about5% of the stabilization compounds, these amounts having been found toimpart the optimum desired improvements in the electrical insulating andthermal stability properties of the cellulosic insulation.

Second, the stabilizing compound or compounds, it more than one is used,must be present in substantially uniform distribution, intimatelypresent throughout the interstices of the fibers comprising thecellulosic insulation, to obtain optimum benefits. This requirement isreadily satisfied because of the fact that (1) all of the members of thegroup of stabilizing compounds of the invention excepting to some degreeammelide, are substantially soluble in water or water alcohol solutionsthus facilitating uniform and thorough incorporation into the celluloseinsulation from 'such solutions, and (2) these v, compounds aresubstantially oil insoluble thus preventing depletion of the uniformdistribution of the stabilization compound in the cellulosic insulationin the presence of oil type dielectrics. To maintain the high dielectricproperties and mechanical strength it is requisite that the stabilizingcompounds be closely associated at all times with the cellulosic fibersto obtain the hereinbefore discussed benefits particularly where theinsulation is to be immersed in a liquid dielectric such as oil duringuse. Where, for example, the stabilizing materials are merely suspendedin the dielectric, an extended period of time elapses before thestabilizers permeate the cellulosic insulation and function at maximumeffectiveness.

As mentioned hereinbefore since. substantially all th members of thegroup of stabilizing compounds in the invention possess a suitabledegree of solubility in water or water-alcohol mixtures, they may bedesirably incorporated in the insulation during its manufacture orfabrication. In the case of paper insulation, particularly, incorpassedbetween calendar rolls to impart a particular surface finish or densityand finally it is rolled for storage and shipment. Also, generally, thedrier is split so that the paper web is partially dried in the firstportion thereof and is finish dried in the second portion. Between thesetwo drying sections of heated rolls a tank is positioned for applicationof sizing materials to the paper.

In practicing the present invention with respect to paper insulation thestabilizing compounds, in substantially aqueous solution, are present inthe conventional sizing tank. The partially dried paper is passedthrough the aqueous solution and, by means of appropriate adjustments inthe concentration of the solution, the paper absorbs a predeterminedamount of stabilizing compounds. In this respect it is to be noted thatit may be necessary to adjust the temperature of the solution in orderto obtain desired concentration. Usually solution temperatures of about60 to 90 C. are adequate to produce a suitably concentrated solution.After this treatment the paper passes through the second portion of thedrier. The temperature of the rolls is determined by trial so as toobtain suflicient paper drying and avoid sticking to the calendar rolls.The process is applicable to either the Fourdrinier or cylinder typepaper-making machine. The dried paper contains the stabilizing compoundsuniformly distributed throughout its interstices.

-In order to more fully describe some of the benefits obtained bypracticing the invention reference should be had to Table I which listsmechanical strength retention of treated paper for the stabilizationcompounds of the invention together with the mechanical strengthretention for untreated kraft paper for comparison purposes. In eachcase, 3% by weight of the particular stabilizing compound was added tokraft paper during its manufacture. In most instances the paper wasabout 5 mils thick and had a density of approximately one. Each of thesamples of paper was wound with enameled wire into a coil and sealed ina tank filled with transformer oil. Strips of transformer core iron werealso placed in the tank. Suflicient current was circulated through thecoil to generate temperatures of 140 C. The coil unit was removed afterseven days and a Mullens bursting strength test run on the aged paper.Table I lists the percent strength retention of the aged sample ascompared to the pro-aging Mullens bursting strength. It is to be notedthat there is some direct relation between mechanical strength retentionand dielectric integrity retention for the cellulosic materials of theinvention in that where the treated cellulosic material exhibits a highretention of mechanical strength, such 4 as the treated paper indicatedin Table I, it also exhibits corresponding high retention of dielectricintegrity.

TABLE I Stabilizing agent: Percent retention *1,S-dihydroxyanthraquinone87 *p-Phenylazoaniline 86 Ammelide 85 *1,3-dimorpholino-2-pr-opan0l 94*Triallylcyanurate 96 2-aminothiazole 85 *Polyvinylpyrrolidone 88 Theasterisks in Table I indicate preferred stabilizing compounds since thepaper treated therewith retains over 85% of its original Mullensbursting strength. Good stabilization of paper insulation will beobtained when the paper contains as little as 0.02% to as much as 10% ofthese stabilizers.

As an illustrative example of an embodiment of the stabilizing compoundsof the invention in an electrical apparatus, a transformer is wound in amanner as illustrated in FIG. 1 using paper treated in accordance withthe invention containing 3% by weight of one or more of the stabilizingcompounds disclosed in the invention.

Referring now to FIGURE 1, the numeral 10 represents the treated kraftpaper which is wound around the individual coils and which is woundbetween the high and low voltage coils of the transformer. Thus, thetransformer coil comprises low voltage coils 14 and 16, as well as highvoltage coils 18, 20 and 22,v insulated by layer-tolayer application ofthe treated paper. In addition, the low voltage coil 14 is insulatedfrom the treated windingtO-Winding by insulation 24. The electricalconductors employed may comprise enameled wire which resists softeningat temperatures of up to 250 C. Suitable enamels are epoxy resinenamels, polyester resin enamels such as isophthalateglycol-maleateresins, silicone modified enamels and polyvinyl formal-phenolic resinenamels.

These enamels may be applied directly on top of wire or may be employedwith asbestos or glass fiber wrapping or other fibrous materials. In thefinished transformer, a liquid dielectric such as oil or a chlorinatedaromatic dielectric, will fill the channel 26 and will, as well,completely permeate the paper insulation. Subsequent to being wound andassembled the entire assembly is vacuum treated to remove air andmoisture from the paper and the coil is thereafter baked to eliminatefully any moisture.

Referring to FIGURE 2, a transformer is prepared in accordance with thepresent invention. The transformer comprises a tank 28 carrying asupport 30 internally on which magnetic core 32 and a coil 34 aredisposed. Coil 34 comprises a high voltage winding 36 and a low voltagewinding 38, each insulated with a wire enamel composition which resistssoftening at temperatures up to 250 C. The turns of the windings 36 and38 are insulated by Wrappings comprising the stabilized cellulosicinsulation of the invention. The windings are also insulated from oneanother by stabilized cellulosic insulation 40, prepared according tothe present invention, which comprises paper, cotton or other cellulosicinsulation. An exterior cellulosic wrapping 42 of cloth or paper may beapplied to the coil 34. In some cases, pressboard, wood or cardboardspacers or various other cellulosic products may be applied to theelectrical windings. A liquid dielectric 44 is disposed within the tank28 to cover the core 32 and coil 34 in order to insulate them and todissipate the heat produced in operating the transformer. The treatedcellulosic materials of this invention retain their dielectricproperties and mechanical strength when in contact with a liquiddielectric containing a small amount of an oxidation inhibitor, such asp-tert-butyl phenol.

FIGURE 3 illustrates an electrical conducting cable comprising anelectrical conductor 50 having cellulosic sheath covering 54; Thecellulosic insulation 52 is stabilized material which has been treatedaccording to the present invention.

It is to be noted with regard to the application of the invention totransformers that transformer construction may be more solid and tighterbecause the treated cellulosic spacers and other components will loseless than half the thickness loss on thermal aging exhibited byuntreated pressboard, kraft paper or other cellulosic materials.

It has also been found that where certain properties are desired, suchas higher initial tensile strength of cellulosic insulation andwaterproofness, that certain resins can be incorporated in the paper inthe process of beating the pulp. These resins can be introduced infinely divided or emulsified form in the beating of the pulp or they canbe introduced later from organic solution. Small amounts of up toseveral percent of resins such as phenolic, epoxy, acrylic,diallylphthalate, etc., have been found to be compatible with thestabilizing compounds of the invention and further enhance mechanical,electrical and thermal stability in the finished product.

It is to be noted that the cellulosic insulation stabilizing compoundsof the invention may be used singly or in combination with one another,or further, in combination with these or the stabilizing compoundsdisclosed in co pending patent applications Ser. No. 164,113, filed Jan.3, 1962 and Ser. No. 839,166, filed Sept. 10, 1959 and itscontinuation-impart Patent 3,102,159 issued Aug. 27, 1963, orapplication Ser. No. 319,387 (Westinghouse Case 34,984), filedconcurrently herewith.

It is to be understood that the above description and drawings areillustrative and not in limitation of the invention or its application.

What is claimed is:

1. An improved sheet cellulosic product having increased stability andresistance to thermal deterioration and particularly adapted for use inelectrical apparatus in combination with a fluid dielectric impregnantin contact with the cellulosic product, the cellulosic productcomprising cellulosic fibers in sheet form, the sheet having uniformlydistributed therethrough from about 0.02% to about by weight based onthe weight of the cellulosic fibers, of at least one stabilizingcompound selected from the group consisting of1,5-dihydroxyanthraquinone, p-phenylazoaniline, ammelide,1,3-dirnorpholino-Z-propanol, triallylcyanurate, 2-arnino-thiazole,polyvinylpyrrolidone.

2. The improved sheet cellulosic product of claim 1 having increasedstability and resistance to thermal de terioration and particularlyadapted for use in electrical apparatus in combination with a fluiddielectric impregnant in contact with the cellulosic product wherein thesheet has uniformly distributed therethrough from about .5 to about 5%by weight based on the weight of the cellulosic fibers, of at least onestabilizing compound selected from the group consisting of1,5-dihydroxyanthraquinone, p-phenylazoaniline, ammelide,1,3-dimorpholino- 2-propanol, triallylcyanurate, 2-aminothiazole,polyvinylpyrrolidone.

3. 'In an electrical apparatus comprising in combina tion a containerand disposed therein an electrical conductor winding provided With ahard, tough flexible enamel coating which resists softening attemperatures up to about 250 C. and cellulosic electrical insulationsubstantially disposed around the winding, the improvement whichcomprises providing from about 0.02% to 10% by weight, based on theweight of the cellulosic electrical insulation, of a stabilizingcompound, the stabilizing compound being uniformly distributedthroughout the cellulosic electrical insulation, and a liquid dielectricconsisting essentially of a petroleum hydrocarbon oil in the saidcontainer surrounding at least part of said electrical conductor windingand substantially completely permeating said cellulosic electricalinsulation,

the said stabilizing compound serving to improve the resistance of thecellulosic insulation to thermal deterioration when heated in thepresence of the said liquid dielectric, the said stabilizing compoundcomprising at least one compound selected from the group consisting of1,5- dihydroxyanthraquinone, p-phenylazoaniline, ammelide,1,3-dimorpholino-Z-propanol, triallylcyanurate, 2-aminothiazole,polyvinylpyrrolidone.

4. The improvement for electrical apparatus of claim 3 wherein the saidliquid dielectric contained in said electrical apparatus contains anoxidation inhibitor.

References Cited OTHER REFERENCES The Condensed ChemicalDictionaryfiSixth edition, Reinhold Publ. Co., N.Y., 1962, QDSCS, page900.

LEWIS H. MYERS, Primary Examiner.

D. A. KETTLESTRINGS, H. HUBERFELD,

Assistant Examiners.

1. AN IMPROVED SHEET CELLULOSIC PRODUCT HAVING INCREASED STABILITY ANDRESISTANCE TO THERMAL DETERIORATION AND PARTICULARLY ADAPTED FOR USE INELECTRICAL APPARATUS IN COMBINATION WITH A FLUID DIELECTRIC IMPREGNANTIN CONTACT WITH THE CELLULOSIC PRODUCT, THE CELLULOSIC PRODUCTCOMPRISING CELLULOSIC FIBERS IN SHEET FORM, THE SHEET HAVING UNIFORMLYDISTRIBUTED THERETHROUGH FROMABOUT 0.02% TO ABOUT 10% BY WEIGHT BASED ONTHE WEIGHT OF THE CELLULOSIC FIBERS, OF AT LEAST ONE STABILIZINGCOMPOUND SELECTED FROM THE GROUP CONSISTING OF1,5-DIHYDROXYANTHRAQUINONE, P-PHENYLAZOANILINE, AMMELIDE,1,3-DIMORPHOLINO-2-PROPANOL, TRIALYLCYANURATE, 2-AMINO-THIAZOLE,POLYVINYLPYRROLIDONE.